Variable capacitator in paralell to loading coil - good idea?
For tuning an LF-transmission antenna a coil, in which one can screw in and out a ferrit core would be the best choice, as it allows to change the inductive value continously. 137.780 ACTIVITY TONIGHT
However such coils are difficultly available ( does someone know where to buy such coils in Europe?), so I have the idea that one could tune the loading coil with a variable capacitaor awitched in paralell to it, which would have the same effect as using a coil L' with a value 1/((1/2*pi*f*L)-2*pi*f*C))*2*pi*f .
Would it be a good idea to do the tuning with a variable capacitator switched in paralell to the loading coil?
Posted by John W1TAG on January 02, 2015 at 00:02:26.
Bill DeCarle's grabber is presently showing WD2XNS, MP, WH2XIL and
WD2XES huddled around 137.780 kHz.
John, W1TAG/WD2XES 470 kHz Activity, Too
Posted by John Davis on January 02, 2015 at 00:12:44.
In reply to 137.780 ACTIVITY TONIGHT posted by John W1TAG (Fwd from qth.net by KD4IDY) on January 02, 2015
Mark Dittmar ABØCW has also announced plans to put his newly modified license for WG2XNI into use on 470 khz tonight (1 Jan) sending regular CW mode, around 9 - 11:30 pm MST or perhaps a bit earlier. He's running about 80 watts into an inverted L.
Bulgaria, 261 closed down
Posted by Mike Terry on January 02, 2015 at 10:51:10.
Rémy Friess reports on various newsgroups:
Hi everyone,
Bulgaria has apparently ended its transmissions on 261 kHz on Dec 31st.
Yet another one that goes... Soon the LW band will be a desert land...
Re: Variable capacitator in paralell to loading coil - good idea?
Posted by John Davis on January 02, 2015 at 19:00:02.
In reply to Variable capacitator in paralell to loading coil - good idea? posted by Hernan on January 01, 2015
In principle, the idea could work over a limited tuning range. I believe the main reason we don't see it done in practice is that, the greater the apparent inductive reactance one tries to obtain in this way, the greater becomes the contribution of the parallel capacitor toward resonating the coil on its own. That causes the tuning to be disproportionately sensitive, could result in phase distortion of modulation sidebands, may interact with the self-resonant frequency of the coil itself, and will result in less suppression of harmonic energy. Think of the frequency response of a second-order single-zero elliptical low pass filter with an exaggerated peak just below the turnover frequency and poor out-of-band suppression beyond the null...that's what the response curve of this type of network would look like.
There are times when it is appropriate to simulate a larger value of coil in this manner; for example, when attempting to achieve an impedance match to the reactance of a medium wave broadcast antenna that is working just slightly off its natural resonant frequency. In that case, such a network helps offset the wide impedance variation that occurs from one side of the carrier frequency to the other, helping to flatten the frequency response and group delay characteristics of the audio sidebands. Even in that situation, the adjustment of the tuning network is quite critical, and is best done for a single operating frequency.
There is a similar approach to what you suggest that is somewhat less sensitive to tuning variations. Connecting the tuning capacitor from antenna to ground would allow you to use a fixed coil of just slightly less inductance than is required to resonate the antenna at the highest frequency of interest. You could then tune from that frequency on downward over a modest range of frequencies. (You could add still more capacitance, but beyond a certain point, more current would flow through the tuning capacitor than the antenna.) The response curve of this tuning arrangement is less critical, more closely resembling that of a pi-network.
The most popular tuning arrangement among LowFER operators here in the US has been variometer coils, which can be very efficient and are only moderately difficult to construct.
John
Range of MF-transmitters working according FCC Part 15 regulations
Posted by Hernan on January 03, 2015 at 06:15:15.
How far can a MF-transmitter working according FCC Part 15 regulations transmit its signal? Really 1 kilometres as http://www.sstran.com/pages/AMT3000/overview.html suggest? Re: Range of MF-transmitters working according FCC Part 15 regulations
If yes, would this also work with a Spitfire AM transmitter in the same way or what must I do to do it with a Spitfire?
Posted by John Davis on January 03, 2015 at 18:22:20.
In reply to Range of MF-transmitters working according FCC Part 15 regulations posted by Hernan on January 03, 2015
The SSTran estimate is very optimistic. On a very quiet channel, over soil of good conductivity, an AM signal from a fully Part 15 compliant transmitter and antenna system is just barely audible at 1 km. It would not be a very enjoyable signal for prolonged listening. If the soil conductivity is low, then you might achieve only half that range, as was true of a transmitter I operated in a region of rocky ground some years ago. And, in the presence of electrical noise or co-channel interference from distant licensed broadcasters--especially if the channel is susceptible to skywave interference--your range might decrease to a hundred metres or less, as was the case after sunset with the installation I had.
Any transmitter with the same input power should yield the same range with the same type of antenna. There have been claims of greater range by some manufacturers, but those all appear to have employed antennas which simply do not comply with the Part 15 Rules.
Of course, Morse code or extra-slow transmission modes such as QRSS offer considerable improvement in range due to their narrowband nature. Several kilometres are possible on mediumwave in the daytime, on a quiet channel with a good receiver, and a few hundred km at night. A quiet channel is very hard to find these days, however.
John
9ZS in Jan 2015 Lowdown
Posted by Joe K9ATG on January 03, 2015 at 20:12:11.
I am SO honored to see 9ZS mentioned in the January 2015 Lowdown. Thank you for its recognition in the magazine.
John, I have numerous photos, sources and details about the original 9ZS and its operator, G.F. Johnson that I would be happy to pass on to you if it would help with your forthcoming article. BTW, I'm still working on a 9ZS page on my website and will send the URL when it is complete.
e mail - joearmstrong comcast net (or above).
Thanks again,
Joe K9ATG
Re: 9ZS in Jan 2015 Lowdown
Posted by John Davis on January 03, 2015 at 21:09:25.
In reply to 9ZS in Jan 2015 Lowdown posted by Joe K9ATG on January 03, 2015
Thanks, Joe. We're always glad to know the origin of a beacon's call sign, and especially when it has a historical connection to such a prominent early longwave station. I'll be contacting you shortly about the additional information.
John
Ferrit coils as loading coils for short MF-transmission antennas
Posted by Hernan on January 04, 2015 at 01:00:09.
Ferrit coils are common as reception antenna for VLF/LF/MF. But are ferrit coils a good choice for loading coils for short MF-transmission antennas? Spektrogram from the end of broadcasting of Donebach transmitter
If not, why? If some types are suitable, which types can be used?
Posted by Harald on January 05, 2015 at 00:01:41.
In the night from December 31st, 2014 to January 1st, 2015 I documented the end of transmission of "Deutschlandfunk"-transmitter Donebach on 153 kHz. I made for this by using "Spec Lab" a spectrogram of the audio signal, which I filmed with the software "Movavi Screen Capture" from the screen without using a camera.
The results can be seen on
https://www.youtube.com/watch?v=lZCLRFUTe3U (long video)
https://www.youtube.com/watch?v=7n3bt2UPeFo (short video from the shut-off)
However this was not the last transmission of Donebach transmitter on 153 kHz. When I drove home from the Sylvester party on January 1st, 2015 at 6 o'clock, it was again on the air, but at least at 8 o'clock on January 1st, 2015 it was finally(!?) shut-down.
Re: Spektrogram from the end of broadcasting of Donebach transmitter
Posted by John Davis on January 05, 2015 at 06:32:53.
In reply to Spektrogram from the end of broadcasting of Donebach transmitter posted by Harald on January 05, 2015
Thanks, Harald. That looks like an interesting way to make video clips, by the way.
For those who remember Harald's chart of longwave broadcast tower heights and types--and those who may not--it is currently at:
http://lwca.org/library/global/LW_broadcast/lwdr1.gif
If your Web browser has automatic picture resizing turned on, you may need to turn it off in order to view the chart at its full size and scroll around within it to see all the details.
John
A good time to listen...
Posted by Mike Terry on January 05, 2015 at 10:27:53.
The national weather forecast for Monday, January 5th calls for arctic air that will soon bring dangerously cold weather to many parts of the U.S. in the next few days.
http://www.13newsnow.com/story/weather/2015/01/04/cold-arctic-blast-polar-vortex/21257707/
Could help AM propagation, even if not is a good time to be indoors listening to the radio.
Keep warm!
Wm Beacon temporarily off-air
Posted by Mike - N8OOU on January 05, 2015 at 15:01:23.
I will be shutting the Wm Beacon down today (1/5/15), to do some relocation of equipment and antenna. I will be making a number of changes so I have no prediction of the final results. My intent is to improve it's signal, and change it over to solar power. The new antenna location will be more in the clear on my property, but not in it's final location. I will post a follow-up when the changes are complete.
Thanks for reading and listening. Mike - OOU
Re: Ferrit coils as loading coils for short MF-transmission antennas
Posted by robert on January 05, 2015 at 23:00:43.
In reply to Ferrit coils as loading coils for short MF-transmission antennas posted by Hernan on January 04, 2015
i have a part 15.219 compliant Medium Wave transmitter i built form a kit that uses a ferrite toroid as the output loading coil to load a 102" CB whip. as far as i know they are more efficient than a linear air coil. it uses a class E output as well as the toroid output coil.
Re: Range of MF-transmitters working according FCC Part 15 regulations
Posted by Robert on January 05, 2015 at 23:09:43.
In reply to Re: Range of MF-transmitters working according FCC Part 15 regulations posted by John Davis on January 03, 2015
i have an SSTRAN AMT5000 in my possession it seems to work slightly better than the industry standard am 1000 rangemaster.
i adjust and tune it up for maximum F/S using a FIM (Nems Clarke 120E) and then adjust the input to 100mW DC input using a DMM.
even without a ground (and properly adjusted to fcc regs) it goes about 1500ft to a good SW portable.
it is available as it is surplus to my needs i live in an apartment and don't have the space to put down a full ground radial system to make it work efficiently.
if anyone has an interest in it but doesn't feel like assembling one yourself i will be glad to let it go for $350.00 shipped
kc8gpd@hotmail.com
Re: Range of MF-transmitters working according FCC Part 15 regulations
Posted by Robert on January 05, 2015 at 23:17:25.
In reply to Re: Range of MF-transmitters working according FCC Part 15 regulations posted by Robert on January 05, 2015
Ps: the reason i use a FIM as opposed to a DMM in the initial tuneup process is the TX is Class E and using a FIM or relative F/S meter to peak the Rf output before setting it to 100mW input seems to get it the closest to it's proper class E operation.
Re: Ferrit coils as loading coils for short MF-transmission antennas
Posted by Robert on January 05, 2015 at 23:22:41.
In reply to Re: Ferrit coils as loading coils for short MF-transmission antennas posted by robert on January 05, 2015
here is a picture of the one i have showing prominently it's toroidal (I Believe it's ferrite) Loading Coil
not sure if you are talking about a loop stick or a toroid coil. the loop stick would not be any where near as efficient for transmission as the toroid.
Re: Ferrit coils as loading coils for short MF-transmission antennas
pic here..
http://www.sstran.com/pages/AMT5000/AMT5000_assembled_board_.jpg
Posted by John Davis on January 06, 2015 at 06:10:03.
In reply to Re: Ferrit coils as loading coils for short MF-transmission antennas posted by Robert on January 05, 2015
In terms of RF resistive loss, a ferrite toroid will not be as efficient (have as high a Q factor) as a well designed air core coil because of loss factors inherent to the use of a ferrite material in close proximity to the winding, especially if high RF voltages are present. Fortunately, at mediumwave frequencies and at the RF power levels in question, the difference in loss is not terribly significant, so a ferrite toroid may indeed be useful. The toroid can be made a lot more compact than a high-Q air core coil, for instance, and that's probably the main reason it is used in the transmitter Robert mentioned.
I also agree with Robert about the inadvisability of trying to employ a conventional ferrite loop stick coil. The main reason there is the wire of the winding itself. I have used ferrite rods inside windings made of larger diameter wire to produce adjustable loading coils of moderate inductance, with some success, but it was a physically awkward arrangement.
John
Re: Ferrit coils as loading coils for short MF-transmission antennas
Posted by Robert on January 06, 2015 at 16:00:57.
In reply to Re: Ferrit coils as loading coils for short MF-transmission antennas posted by John Davis on January 06, 2015
here is a design for a good linear coil base loaded design.
http://filebay1.home.comcast.net/~filebay1/antenna.html
it is fixed at 1700 kHz
i have thought about modifying the design using a varometer type coil to make it variable while still maintaining decent efficiency.
when put at ground level with an 8ft ground rod at the base along with a buried radial set i believe it's efficiency is pretty high for these 3m shortened verticals (at least that is what i have been told by the guy who designed it).
i know with 100mW input there was a guy ranging about 1.5-2 miles ground wave (although the signal at the fringe had much static but signal still intelligible) with one over in manteca, ca
Hifer GNK
Posted by Brian nb9e on January 08, 2015 at 23:46:57.
Nice copy on Hifer GNK here at the work qth DN10tx right now !!! Brian nb9e
EH hifer
Posted by Sal,K1RGO on January 09, 2015 at 22:33:40.
I discovered an intermittent 2N3906 output transistor on the hifer rig and replaced it. So if EH was absent, that was the issue. This may have been going on for a while.
All looks ok for now. Lowfer band is still full of noise, no luck yet even with the noise nuller.
later..............Sal,K1RGO
Variable inductivities - where to buy?
Posted by Hernan on January 09, 2015 at 23:25:03.
Where can I best get variable inductivities or cores for manufacturing such inductivities? I search for coils with screwable ferrit core as this is the most convenient way for such device.
How best to tune a Spitfire AM-transmitter to short antenna
Posted by Solsim on January 10, 2015 at 05:55:10.
Which is the best external network to tune a Spitfire AM-transmitter to a 3 metres long antenna?
Re: How best to tune a Spitfire AM-transmitter to short antenna
Posted by Webmaster on January 10, 2015 at 07:28:50.
In reply to How best to tune a Spitfire AM-transmitter to short antenna posted by Solsim on January 10, 2015
I'm sorry, but it does not appear that any regular users of this forum have a specimen of this transmitter. Most of our group are involved with Morse code or digital transmissions under Part 15 Rules in the U.S., for which this is clearly not the ideal transmitter.
(Nor is it strictly legal in this country. It is not sufficient for a manufacturer to simply state that their transmitter "complies" with Part 15. There are specific requirements for certification, including obtaining an FCC identification number. Without that, it is not legal to import the unit or sell it here. I also observe on the manufacturer's Web site that they are aware it is not legal to sell it for ANY on-air use in the EU, either.)
Even if someone has the means to assemble the unit and test it properly for compliance and self-certification at home, it is unfortunate that the manufacturer does not provide any online information about its use, including specifics about antenna construction and tuning. They do say that is has an internal tuning arrangement, and suggest that it can be used with an external one, but they provide no further technical requirements. I notice that appears to be a common complaint in other forums that are more oriented toward microbroadcasters. Consumers ought to have access to such information before deciding to purchase, in my view.
A Google search will quickly turn up some of those other sites, and even a YouTube video or two showing the device in use. Just be aware that some sites profess to be about "Part 15," but many of their participants have little knowledge of and/or no regard for the Part 15 Rules.
John
Re: Wm Beacon temporarily off-air
Posted by Mike - N8OOU on January 10, 2015 at 17:37:38.
In reply to Wm Beacon temporarily off-air posted by Mike - N8OOU on January 05, 2015
I have put the beacon back on the air and am posting this update.
The list of things I changed include switching the P.A at the antenna to Gel Cell / Solar power. I moved the antenna farther away from the metal buildings, towers, and other antennas. The tophat has been raised in height by 15 ft. or so, and a real ground system is in place with 8 radials ranging from 50 to 190 Ft.
I have also re-worked the Low Pass Filter in the P.A. as sometime before Christmas several components failed.
This installation is still another temporary location in the plan for the beacon. I have a couple more antenna ideas to try in this location before moving it to it's permanent home in a more open space on the property. world ndb/beacon identification website
Posted by john on January 20, 2015 at 05:46:27.
hi, can someone please post the link to the worldwide ndb/beacon identification website. it was a one stop website for any beacon in the world and people could actually log the stations they heard. Its been awhile and I can't seem to remember it.
thanks john
Re: world ndb/beacon identification website
Posted by Geek on January 20, 2015 at 06:13:28.
In reply to world ndb/beacon identification website posted by john on January 20, 2015
Not worldwide, but this is the one I use: Re: EH hifer
http://www.dxinfocentre.com/ndb.htm
Posted by Geek on January 20, 2015 at 06:16:32.
In reply to EH hifer posted by Sal,K1RGO on January 09, 2015
LowFER'ing has been a bust for me this season so far :-(
hifers today
Posted by Sal,K1RGO on January 20, 2015 at 15:54:13.
Well conditions could be better, only USC and SIW were copied with QSB today at 0350 utc. Re: world ndb/beacon identification website
As for lowfer band ,I am plagued with noise but I think I have got bits of TAG at times.
later......Sal, K1RGO
Posted by Webmaster on January 21, 2015 at 00:50:34.
In reply to Re: world ndb/beacon identification website posted by Geek on January 20, 2015
You're probably thinking of http://www.classaxe.com/dx/ndb/rna/, John.
If you should ever forget or misplace it, it's always listed on our home page at lwca.org.
JH Lowfer update
Posted by John Hamer on January 21, 2015 at 03:20:21.
Hey Guys, I have not had a chance to get JH running yet this year. I have been busy with projects around the house. I did get some pictures uploaded to my website if anyone is interested. You can see all the trees I'm dealing with. I do still plan on making my antenna taller and adding a better ground radial system. I will give an update when I am back on the air. My site is JWHamer.me. The server is at my house so I apologize for slow/lost connections.
Wm Beacon Website
Posted by Mike - N8OOU on January 22, 2015 at 03:51:50.
Hello all;
I am announcing a website for the Wm Lowfer Beacon. I have put a bit of its history, first time reception reports, status, and some technical information about the station. I will continue to update and add to the pages, as time allows.
You can access the site at this url ====> wmbeacon.meekfarm.us
Thanks for looking. Mike N8OOU
Re: Wm Beacon Website
Posted by John Hamer on January 22, 2015 at 17:41:12.
In reply to Wm Beacon Website posted by Mike - N8OOU on January 22, 2015
Very Nice!
Re: world ndb/beacon identification website
Posted by john on January 23, 2015 at 05:27:19.
In reply to Re: world ndb/beacon identification website posted by Webmaster on January 21, 2015
thats it!! thank-you so much.
john
Re: Wm Beacon Website
Posted by Joe K9ATG on January 26, 2015 at 01:06:05.
In reply to Wm Beacon Website posted by Mike - N8OOU on January 22, 2015
Nice site, Mike! The graphics and the description are very interesting, but the attention given to Bill Ashlock was particularly appreciated.
Hope to get a chance to tune in soon, Joe
MLS STATUS
Posted by Mark on January 28, 2015 at 14:58:27.
Hi all, Beacon on 477.7
Beacon MLS @ 186.204 is still working ok after the replacement of the failed part in the filter. The base insulator was deep in the snow yesterday but I dug it out and along with the connecting cable to the box are now clear and dry. I plan on keeping the beacon on line till early April running QRSS30. Thanks... Mark
Posted by Joe on January 29, 2015 at 02:23:35.
Hello all,
A beacon is running tonight and tomorrow on 477.7 kHz from GN37, 12 WPM CW and a 5 second carrier. Reports are most welcomed.
73 Re: world ndb/beacon identification website
Joe VO1NA
Posted by Steve on January 30, 2015 at 15:41:45.
In reply to Re: world ndb/beacon identification website posted by Webmaster on January 21, 2015
Thanks, from me , also....Steve
potrzebie
